Hardenable, fluorinated copolymer process for its manufacture and its application in varnishes and paints

ABSTRACT

A hardenable fluorinated copolymer of fluorinated monomers and an acrylamide derivative and paints, paints and varnishes comprising such copolymers, and the process of making such hardenable copolymer.

This application is a division of application Ser. No. 07/693,132 filedApr. 29, 1991, which in turn is a division of application Ser. No.07,511,566, filed Apr. 20, 1990, now U.S. Pat. No. 5,037,922.

BACKGROUND OF THE INVENTION

The present invention pertains to a hardenable, fluorinated copolymer ofvinylidene fluoride (C₂ H₂ F₂), at least one fluorinated monomerselected from tetrafluoroethylene (C₂ F₄), chlorotrifluoroethylene (C₂F₂ Cl) or hexafluoropropylene (C₃ F₆), and an acrylamide derivative.This copolymer, which is soluble in organic solvents, is particularlyrecommended for the manufacture of paints and varnishes.

Fluorinated polymers are known for their good mechanical properties andtheir excellent resistance to chemical products and weather.Nevertheless, their insolubility in conventional solvents makes themunusable for certain application such as, for example, that as a resinfor paints and varnishes where their properties are sought for themanufacture of coatings with good chemical and weather resistance andeasy maintenance.

In order to profit from the desirable properties of the fluorinatedpolymers while avoiding their drawbacks, means were sought to make themsoluble in conventional organic solvents. In order to achieve this, itis known to decrease the crystallinity of fluoride-containing polymersby copolymerization of monomers unsaturated in the ethylene position, ofwhich monomers at least one is fluorinated.

In addition, to use such copolymers it is desirable for certainapplications, particularly for their application in the manufacture ofpaints and varnishes, to preserve for them a sufficient degree ofrigidity and to make them hardenable by incorporation of functionalgroups into their structure.

Such hardenable, fluorinated copolymers are described in French Patents2,597,873 and 2,569,703. These products are obtained by copolymerizationof chlorotrifluoroethylene, a fatty acid ester, and hydroxylated orethoxylated allyl glycidyl ether. These copolymers can possibly containless than 20% of another, non-fluoride-containing comonomer. If thesecopolymers contain more than 20% of the preceding comonomer, they losetheir solubility in solvents and their transparency. In addition, theintroduction of fluorine by the use of chlorotrifluoroethylene alonealso brings with it the chlorine-containing element which is notdesirable in large amounts for the optical properties and resistance tocorrosion.

In JP 59-174,657/84, there is also described a hardenable copolymerbased on vinylidene fluoride, tetrafluoroethylene,chlorotrifluoroethylene, a vinyl ester and a hydroxylation agent. Thiscopolymer, which contains less than 45% of vinyl ether fluoride and isbased on vinyl ester, has the drawback of yielding after hydrolysis arather strongly colored copolymer solution, which damages thetransparency of the subsequently prepared varnishes.

SUMMARY OF THE INVENTION

The object of the present invention is a fluorinated copolymer, which iseasily hardenable in the hot state in the possible presence of ahardening agent. When dissolved in an appropriate solvent, thiscopolymer may be used as a paint or varnish to form coatings which arehard, stable and transparent in the absence of pigments and which adherewell to metals and glass.

The hardenable copolymer in accordance with the invention, whichcontains the copolymerization radicals of a fluorinated monomer and anacrylamide derivative is characterized in that:

(i) the fluorinated monomer radicals originate from the association ofvinylidene fluoride and another fluorinated monomer selected from amongtetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, orthe mixture of at least two-of these three monomers, and

(ii) in that the acrylamide derivative is selected from compounds offormula: ##STR1## in which: R=H, CH₃, ##STR2## with: n representing anumber from 0 to 8,

and x representing a number from 0 to 3.

DETAILED DESCRIPTION

With respect to the copolymer, the association for 100 moles of thetotality of fluorinated monomers is usually formed of:

(i) 50 to 98 moles of vinylidene fluoride, and

(ii) 2 to 50 moles of the other fluorinated monomer as defined.

Preferably, the hardenable, fluorinated copolymer in accordance with theinvention is characterized in that it is comprised of monomer radicalsoriginating from:

(i) 50 to 98 moles, preferably 70 to 85 moles, of vinylidene fluoride,

(ii) 2 to 50 moles, preferably 15 to 20 moles, of fluorinated monomerselected from among tetrafluoroethylene, chlorotrifluoroethylene,hexafluoropropylene, or a mixture of at least two of the three monomers,and

(iii) 2 to 30 moles, preferably 5 to 10 moles, of the precedingacrylamide derivative per 100 moles of the totality of fluorinatedmonomers.

Compounds of the following formulas can be cited among the preferredacrylamide derivatives: ##STR3##

It is, of course, not excluded to associate several of these acrylamidederivatives, particularly an alkoxylated derivative and a hydroxylatedderivative.

In order to be able to use these copolymers in a liquid coatingcomposition such as paint or varnish, it is recommended that theinherent viscosity of the copolymer dissolved in dimethyl formamide at25° C. at a concentration of 1 g/dL be within the range of 0.02 to 0.2dL/g.

The copolymer in accordance with the invention is principally obtainedaccording to the known solution polymerization procedures. A procedureconsists of copolymerizing the monomers in a medium which is a solventfor all of the monomers, in the presence of an organosoluble initiator,at a temperature between 30 and 120° C., preferably between 40° and 80°C., under a pressure of approximately 10 to 80 bars, preferably between15 and 40 bars.

In accordance with the invention, the hardenable copolymer is obtainedby copolymerization of vinylidene fluoride, at least one fluorinatedmonomer selected from tetrafluoroethylene, chlorotrifluoroethylene, orhexafluoropropylene and the previously defined acrylamide derivative.The following are employed for 100 moles of polymerized, fluorinatedmonomers:

(i) 50 to 98 moles of vinylidene fluoride, and

(ii) 2 to 50 moles of tetrafluoroethylene or chlorotrifluoroethylene orhexafluoropropylene or a mixture of at least two of the three monomers,with which is associated the previously defined acrylamide derivative.

In order to obtain a hardenable copolymer with the best properties, oneusually associates 2 to 20 moles of the previously defined acrylamidederivative per 100 moles of the totality of the fluorinated monomers.

In accordance with the preferred copolymerization mode, the solvent isheated to the selected reaction temperature in an agitated reactor whichhas first been degassed. A mixture of fluorinated monomers as well as aninitial fraction of the acrylamide derivative are introduced into thereactor.

The amount of monomer mixture to be introduced to reach the selectedreaction pressure depends on the solubility conditions of thefluorinated monomers in the selected solvent. The monomer solvent weightratio is generally between 0.1 and 1.

When the reaction pressure and the reaction temperature are reached, thepolymerization initiator is introduced into the reaction. The formationof polymer is manifested by a drop in pressure which is compensated forby adding fluorinated monomer mixture.

One can add a fluorinated monomer mixture of molar composition identicalto that which was introduced initially. It is also possible to take intoaccount the individual reactivities of each comonomer and adjust thecomposition of the mixture added during polymerization in order tocreate a copolymer of homogeneous composition.

The acrylamide derivative can also be added during polymerization. Thelevel of this derivative added continuously is generally higher than thelevels of acrylamide derivative added initially, to take into accountthe greater reactivity of these derivatives.

The acrylamide derivative is added in such a manner that the compositionof the mixture of fluorinated monomers and acrylamide derivativeintroduced remains constant during the duration of the polymerization.

The addition of monomer mixture for maintaining the pressure iscontinued for a sufficiently long period of time to reach a dry extracton the order of 10 to 60%, preferably 15 to 40%.

The volatile residual monomers can be eliminated by degassing.

The final solution is extracted from the reactor and can be stored inthat form. It can also be concentrated immediately or subsequently inorder to obtain the amount of dry extract selected for the use of thecopolymer.

The solvents selected for the copolymerization reaction must allowsolubilization of the monomer mixture while remaining inert in relationto the other reaction components. They are selected preferably fromamong the acetates and alcohols or their mixtures, ketones, and etheralcohols. Ethyl acetate, butyl acetate, methanol or tertiobutanol areparticularly recommended. When the copolymer is prepared for the purposeof application in formulations for paint or varnish, a mixture of butylacetate and methanol employed as solvent during the copolymerization canmake it possible to obtain directly, without subsequent treatment, acomposition which is usable as it is with, possibly, elimination of themethanol and addition of the complementary additives which are standardfor these types of formulations.

The copolymerization initiators are known per se, the most popular beingselected from among the radical polymerization initiators such as theperdicarbonates, perpivalates and azo compounds, such as diisopropyl ordicyclohexyl percarbonate, tertiobutyl or tertioamyl perpivalate,azobisisobutyronitrile and azo-bis-2,2-dimethylvaleronitrile.

When the cross-linkable copolymer in accordance with the invention is tobe used as the basis for a paint or varnish formulation, it can, as wasalready mentioned, be used as it is in its initial reaction solventmedium. It can also be more or less concentrated and put again intosolution in a solvent which is better adapted to the type of paint orvarnish desired. As is, the copolymer in solvent medium yields acolorless and transparent solution. To this solution can be added thedesired additives such as pigment, fillers, diluents, ultravioletabsorption agent, stabilizing agent or even hardening agent to improvethe hardening reaction via hot cross linking. Among the most well-knownhardening agents can be cited melamine formaldehyde, urea formaldehyde,the epoxides, isocyanates, organic acids or their anhydrides. Thecross-linking temperature of these copolymers is generally between 0°and 260° C. and essentially depends on the chemical nature of thehardener and the conditions of implementation.

The invention will be further described in connection with the followingexamples which are set forth for purposes of illustration only.

EXAMPLE 1

Two liters of methanol are introduced into a 3.3-L autoclave equippedwith effective agitation, which has been degassed under vacuum. Theautoclave is brought to a temperature of 50° C. At this temperature, oneadds 440 g of fluorinated monomer mixture containing vinylidenefluoride, tetrafluoroethylene and chlorotrifluoroethylene to reach 20bars of pressure in the respective molar proportions of 79/15/6.

One then adds 4 g of N-methylolacrylamide and then 5 g of cyclohexylperdicarbonate.

To maintain the pressure at 20 bars, one adds over five hours 540 g offluorinated monomer mixture containing vinylidene fluoride,tetrafluoroethylene and chlorotrifluoroethylene in the respective molarproportions of 79/15/6.

One adds simultaneously and continuously over the same duration ofpolymerization 16 g of N-methylolacrylamide (NMA).

After five hours of polymerization, the autoclave is degassed and onedischarges a transparent copolymer solution which has a dry extract of25%. The copolymer contains fluorinated structural units originatingfrom the vinylidene fluoride, tetrafluoroethylene andchlorotrifluoroethylene in the respective molar proportions of 81/13/7,determined by NMR (nuclear magnetic resonance) of the fluorine 19. Themolar level of N-methylolacrylamide in the copolymer is 2.6 mol.% inrelation to the totality of fluorinated structural units. The inherentviscosity of the copolymer is 0.0437 dL/g.

EXAMPLE 2

Two liters of methanol are introduced into a 3.3-L autoclave equippedwith effective agitation, which has been degassed under vacuum. Theautoclave is brought to a temperature of 50° C. At this temperature, oneadds 436 g of fluorinated monomer mixture containing vinylidenefluoride, tetrafluoroethylene and chlorotrifluoroethylene to reach 20bars of pressure in the respective molar proportions of 79/15/6.

One then adds 13.6 g of methylacrylamidoglycolate methyl ether (MAGME)then 5 g of cyclohexyl perdicarbonate.

To maintain the pressure at 20 bars, one adds over six hours 440 g offluorinated monomer mixture containing vinylidene fluoride,tetrafluoroethylene and chlorotrifluoroethylene in the respective molarproportions of 79/15/6.

One adds simultaneously and continuously over the same duration ofpolymerization 41 g of methylacrylamidoglycolate methyl ether.

After six hours of polymerization, the autoclave is degassed and onedischarges a transparent copolymer solution which has a dry extract of22%. The copolymer contains fluorinated structural units originatingfrom the vinylidene fluoride, tetrafluoroethylene andchlorotrifluoroethylene in the respective molar proportions of 81/13/7,determined by NMR Of the fluorine 19. The molar level ofmethylacrylamidoglycolate methyl ether in the copolymer is 5 mol. % inrelation to the totality of fluorinated structural units. The inherentviscosity of the copolymer is 0.0483 dL/g.

EXAMPLE 3

Two liters of methanol are introduced into a 3.3-L autoclave equippedwith effective agitation, which has been degassed under vacuum. Theautoclave is brought to a temperature of 50° C. At this temperature, oneadds 440 g of fluorinated monomer mixture containing vinylidenefluoride, tetrafluoroethylene and chlorotrifluoroethylene to reach 20bars of pressure in the respective molar proportions of 79/15/6.

One then adds 11.5 g of acrylamidoglycolic acid and then 5 g ofcyclohexyl peroxydicarbonate.

To maintain the pressure at 20 bars, one adds over three hours 350 g offluorinated monomer mixture containing vinylidene fluoride,tetrafluoroethylene and chlorotrifluoroethylene in the respective molarproportions of 79/15/6.

One adds simultaneously and continuously over the same duration ofpolymerization 23 g of acrylamidoglycolic acid.

After three hours of polymerization, the autoclave is degassed and onedischarges a transparent copolymer solution which has a dry extract of17.3%. The copolymer contains fluorinated structural units originatingfrom the vinylidene fluoride, tetrafluoroethylene andchlorotrifluoroethylene in the respective molar proportions of 81/13/7,determined by NMR of the fluorine 19. The molar level ofacrylamidoglycolic acid in the copolymer is 4.1 mol. % in relation tothe totality of fluorinated structural units. The inherent viscosity ofthe copolymer is 0.046 dL/g.

EXAMPLE 4

Two liters of methanol are introduced into a 3.3-L autoclave equippedwith effective agitation, which has been degassed under vacuum. Theautoclave is brought to a temperature of 50° C. At this temperature, oneadds 450 g of fluorinated monomer mixture containing vinylidenefluoride, tetrafluoroethylene and hexafluoropropylene to reach 20 barsof pressure in the respective molar proportions of 75/15/10.

One then adds 13.6 g of methylacrylamidoglycolate methyl ether (MAGME),then 5 g of cyclohexyl perdicarbonate.

To maintain the pressure at 20 bars, one adds over six hours 400 g offluorinated monomer mixture containing vinylidene fluoride,tetrafluoroethylene and hexafluoropropylene in the respective molarproportions of 75/15/10.

One adds simultaneously and continuously over the same duration ofpolymerization 41 g of methylacrylamidoglycolate methyl ether.

After six hours of polymerization, the autoclave is degassed and onedischarges a transparent copolymer solution which has a dry extract of20.5%. The copolymer contains fluorinated structural units originatingfrom the vinylidene fluoride, tetrafluoroethylene andhexafluoropropylene in the respective molar proportions of 79/15/6,determined by NMR of the fluorine 19. The molar level ofmethylacrylamidoglycolate methyl ether in the copolymer is 5.1 mol. % inrelation to the totality of fluorinated structural units. The inherentviscosity of the copolymer is 0.0506 dL/g.

EXAMPLE 5

Two liters of methanol are introduced into a 3.3-L autoclave equippedwith effective agitation, which has been degassed under vacuum. Theautoclave is brought to a temperature of 50° C. At this temperature, oneadds 440 g of fluorinated monomer mixture containing vinylidenefluoride, tetrafluoroethylene and chlorotrifluoroethylene to reach 20bars of pressure in the respective molar proportions of 79/15/6.

One then adds 13.6 g of methylacrylamidoglycolate methyl ether (MAGME),then 4 g of N-methylolacrylamide (NMA), then 75 g of cyclohexylperdicarbonate.

To maintain the pressure at 20 bars, one adds over five hours 440 g offluorinated monomer mixture containing vinylidene fluoride,tetrafluoroethylene and chlorotrifluoroethylene in the respective molarproportions of 79/15/6.

One adds simultaneously and continuously over the same duration ofpolymerization 41 g of methylacrylamidoglycolate methyl ether and 12 gof N-methylolacrylamide.

After five hours of polymerization, the autoclave is degassed and onedischarges a transparent copolymer solution which has a dry extract of22%. he copolymer contains fluorinated structural units originating fromthe vinylidene fluoride, tetrafluoroethylene and chlorotrifluoroethylenein the respective molar proportions of 82/12/6, determined by NMR of thefluorine 19. The molar levels of MAGME and NMA in the copolymer are 5 to2.5 mol. % in relation to the totality of fluorinated structural units.The inherent viscosity of the copolymer is 0.046 dL/g.

EXAMPLE 6

Into a 3.3-L autoclave equipped with effective agitation, which has beendegassed under vacuum, one introduces 2 liters of a 1/1 mixture byweight of methanol and tertiobutanol. The autoclave is brought to atemperature of 50° C. At this temperature, one adds, 550 g offluorinated monomer mixture containing vinylidene fluoride andchlorotrifluoroethylene to reach 20 bars of pressure in the respectivemolar proportions of 85/15.

One then adds 13.6 g of methylacrylamidoglycolate methyl ether (MAGME)and then 5 g of cyclohexyl perdicarbonate.

To maintain the pressure at 20 bars, one adds over six hours 440 g offluorinated monomer mixture containing vinylidene fluoride andchlorotrifluoroethylene in the respective molar proportions of 75/25.

One adds simultaneously and continuously over the same duration ofpolymerization 49.5 g of methylacrylamidoglycolate methyl ether.

After six hours of polymerization, the autoclave is degassed and onedischarges a transparent copolymer solution which has a dry extract of22.5%. The copolymer contains fluorinated structural units originatingfrom the vinylidene fluoride and chlorotrifluoroethylene in therespective molar proportions of 75/25, determined by NMR of the fluorine19. The molar level of methylacrylamidoglycolate methyl ether in thecopolymer is 5 mol. % in relation to the totality of fluorinatedstructural units. The inherent viscosity of the copolymer is 0.069 dL/g.

EXAMPLE 7

The fluorinated copolymer of Example 1 is heated under vacuum untilevaporation of the methanol and then diluted with methyl isobutylketone.

A varnish is prepared by simple mixing of the constituents (in parts byweight):

    ______________________________________                                        (i)     fluorinated copolymer (2.6% of                                                                    100                                                       NMA and 49% of dry extract in                                                 methyl isobutyl ketone)                                               (ii)    partially methylated melamine                                                                     23.3                                                      formaldehyde resin (viscosity                                                 7,000 mPa · s at 90% dry extract                                     in isobutanol)                                                        (iii)   p-toluene sulfonic acid                                                                           0.2                                               ______________________________________                                    

The varnish is applied in 100 μm strokes on a 0.7 mm thick chromatedaluminum support, then baked for 30 minutes at 180° C. to yield a 25 μmthick film. The cross-linkage is evaluated by the methyl ethyl ketone(MEK) resistance test in which a cotton cloth impregnated with methylethyl ketone is rubbed with a back and forth movement over the filmuntil the film is abraded. A number of back and forth strokes between 50and 100 is an indication of good cross-linkage. A number equal to 100 ormore is the indication of excellent cross-linkage. The compatibility ofthe varnish is evaluated on the basis of the transparency of the filmsobtained with:

    ______________________________________                                        E = excellent      total transparency                                         G = good           slight clouding                                            P = poor           translucent film                                           ______________________________________                                    

The film produced above resisted more than 100 back and forth strokeswith MEK and displayed an excellent transparency.

EXAMPLE 8

A paint is prepared under the following conditions:

One mixes 200 g of a solution in methyl isobutyl ketone of the copolymerof Example 7 with 98 g of titanium dioxide and 22 g ofethoxyethylpropionate in a ball mill so as to obtain a grinding pastewith a grinding fineness smaller than 10 μm.

One takes 160 g of this paste and deconcentrates it with 23.3 g ofpartially methylated melamine formaldehyde resin, 0.2 g of p-toulenesulfonic acid and 30 g of ethoxyethylpropionate to yield a white pastewhich has a Ford cup number 4 viscosity of 85 seconds.

This white paint is applied on chromated aluminum with 100 m spiralstrokes and then baked for 30 minutes at 180° C. in order to obtain a 25μm thick film. The paint obtained resists more than 100 back and forthstrokes with methyl ethyl ketone (MEK), has a Gardner luster measured at60° of 42.2%, a class 0 adherence determined according to NFT standard30 038 and is not affected by a 1,000 hour exposure to the Q.U.V. TheQ.U.V. is an accelerated aging device in which the effects of sunlightare reproduced by means of four tubes emitting ultraviolet rays. Thetemperature during the ultraviolet exposure is 63° C. Awater-condensation device makes it possible to maintain the humiditylevel at 100% relative humidity during the condensation phase. Thetemperature of the sample during the condensation phase is 50° C. Thecondensation and irradiation phases, each lasting four hours, arealternated.

EXAMPLE 9

The fluorinated copolymer of Example 2 is heated under vacuum untilevaporation of the methanol and then diluted with methyl isobutyl ketone(MIBK).

A varnish is prepared by simple mixing of the constituents (in parts byweight):

    ______________________________________                                        (i)    fluorinated copolymer (5 mol. % of                                                                    100                                                   MAGME at 50% of dry extract in                                                methyl isobutyl ketone)                                                (ii)   partially methylated melamine for-                                                                    23.8                                                  maldehyde resin (viscosity 7,000                                              mPa · s at 90% dry extract in isobutanol)                     (iii)  p-toulene sulfonic acid 0.2                                            ______________________________________                                    

This varnish is applied in 100 μm strokes on a 0.7 mm thick chromatedaluminum support, then baked so as to reach a minimum plate temperature(MPT) of 250° C. for 45 seconds so as to yield a 24 μm thick, dry film.

EXAMPLE 10

A paint is prepared under the following conditions:

One mixes 200 g of a solution in MIBK of the copolymer of Example 9 with64.2 g of blue cobalt pigment and 31.5 g of ethoxyethylpropionate in aball mill so as to obtain a grinding paste with a grinding finenesssmaller than 10 μm.

One takes 148 g of this paste and deconcentrates it with 23.8 g ofpartially methylated melamine formaldehyde resin, 0.2 g of para-toluenesulfonic acid, and 20 g of ethoxyethylpropionate to obtain a Ford cupnumber 4 viscosity of 80 seconds.

This blue paint is applied on a 0.7 mm thick chromated aluminate platewith 100 μm strokes and then baked so as to achieve a MPT of 250° C. for45 seconds, yielding a 23 μm thick, dry film.

The paint obtained resists more than 100 back and forth strokes withMEK, has a Gardner luster measured at 60° of 44%, a class 0 adherencedetermined according to NFT standard 30 038 and is not affected by a1,000 hour exposure to the Q.U.V.

EXAMPLE 11

The fluorinated copolymer of Example 3 is heated under vacuum untilevaporation of the methanol and then diluted with diacetone alcohol.

A varnish prepared by simple mixing of constituents (in parts byweight):

    ______________________________________                                        (i)    fluorinated copolymer (4.1 mol. % of                                                                100                                                     acrylamidoglycolic acid at 50% in                                             diacetone alcohol)                                                     (ii)   blocked cycloaliphatic polyisocyanate                                                               50.9                                                    (in solution at 60% in n-butylacetate/                                        xylene blocked NCO content 8%)                                         (iii)  dibutyltin dilaurate  0.1                                              ______________________________________                                    

This varnish is applied in 100 μm strokes on a 0.7 mm thick chromatedaluminum plate, then baked at 150° C. for 30 minutes so as to yield a 20μm thick film.

This film endures without damage 100 back and forth strokes with MEK andexhibits excellent transparency.

EXAMPLE 12

The fluorinated copolymer of Example 4 is heated under vacuum untilevaporation of the methanol and then diluted with methyl isobutylketone.

A varnish prepared by simple mixing of the constituents (in parts byweight):

    ______________________________________                                        (i)   fluorinated copolymer     100                                                 (5.1 mol. % of MAGME at 52% of dry                                            extract in methyl isobutyl ketone (MIBK))                               (ii)  partially methylated melamine formalde-                                                                 24.8                                                hyde resin (viscosity 7,500 mPa · s at                               90% in isobutanol)                                                      (iii) p-toluene sulfonic acid   0.2                                           ______________________________________                                    

This varnish is applied in 100 μm strokes on a 0.7 mm thick chromatedaluminum support, then baked at 180° C. for 30 minutes so as to yield a24 μm thick, dry film.

This film endures without damage 100 back and forth strokes with MEK andexhibits excellent transparency.

EXAMPLE 13

The fluorinated copolymer of Example 5 is heated under vacuum untilevaporation of the methanol and then diluted with methyl isobutylketone.

A varnish is prepared by simple mixing of the constituents (in parts byweight):

    ______________________________________                                        (i)   fluorinated copolymer (2.5% NMA +                                                                       100                                                 MAGME at 50% of dry extract in MIBK)                                    (ii)  p-toluene sulfonic acid   0.2                                           ______________________________________                                    

This varnish is applied in 150 μm strokes on a 0.7 mm thick chromatedaluminum support, then baked at 200° C. for 30 minutes so as to yield a19 μm thick, dry film.

This film endures without damage 100 back and forth strokes with MEK andexhibits excellent transparency.

EXAMPLE 14

The fluorinated copolymer of Example 6 is heated under vacuum untilevaporation of the methanol and then diluted with diacetone alcohol.

A varnish is prepared by simple mixing of the constituents (in parts byweight):

    ______________________________________                                        (i)    fluorinated copolymer  100                                                    (5.1 mol. % of MAGME at 55% of dry                                            extract in diacetone alcohol)                                          (ii)   hexamethoxymethylmelamine resin                                                                      9.7                                             (iii)  p-toluene sulfonic acid                                                                              0.2                                             ______________________________________                                    

This varnish is applied in 100 μm strokes on a 0.7 mm thick chromatedaluminum support, then baked so as to reach a minimum plate temperature(MPT) of 250° C. for 40 seconds, yielding a 23 μm thick, dry film.

This film endures without damage 100 back and forth strokes with MEK andexhibits excellent transparency.

While the invention has been described in connection with a preferredembodiment, it is not intended to limit the scope of the invention tothe particular form set forth, but on the contrary, it is intended tocover such alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

What is claimed is:
 1. A process for manufacturing hardenable copolymerbased on fluorinated monomer and acrylamide derivative, comprisingpolymerizing in solution:(a) vinylidene fluoride, (b)tetrafluoroethylene and/or chlorotrifluoroethylene and/orhexafluoropropylene, and (c) an acrylamide derivative of the formula:wherein R is H or CH₃, ##STR4## with: n representing a number from 0 to8, andx representing a number from 0 to
 3. 2. The process of claim 1,wherein for 100 moles of fluorinated monomers, the following areused:(a) 50 to 98 moles represent vinylidene fluoride, and (b) 2 to 50moles represent tetrafluoroethylene, chlorotrifluoroethylene,hexafluoropropylene, or the mixture of at least two of these threemonomers.
 3. The process of claim 2, wherein for 100 moles of thetotality of the fluorinated monomers, the following are used:(a) 50 to98 moles of vinylidene fluoride, (b) 2 to 50 moles oftetrafluoroethylene and/or chlorotrifluoroethylene and/orhexafluoropropylene, and (c) 2 to 30 moles of an acrylamide derivative.4. The process of claim 1, wherein the copolymerization is carried outat a temperature between about 30° and 120° C. in an alcohol, anacetate, or a ketone and at a pressure between about 10 to 80 bars. 5.The process of claim 2, wherein the copolymerization is carried out at atemperature between about 30° and 120° C. in an alcohol, an acetate, ora ketone and at a pressure between about 10 to 80 bars.
 6. The processof claim 3, wherein the copolymerization is carried out at a temperaturebetween about 30° and 120° C. in an alcohol, an acetate, or a ketone andat a pressure between about 10 to 80 bars.